The present invention is related to systems and methods for accessing a magnetic storage medium, and more particularly to systems and methods for controlling access to a magnetic storage medium.
A magnetic storage device typically include a storage medium that carries both stored data and synchronization information. The synchronization information is placed at intermittent locations across the storage medium and is periodically accessed to aid in identifying the location of a read/write head assembly in relation to the storage medium. FIG. 1A depicts an exemplary set of synchronization information generally referred to as a servo data sector 100. As shown, servo data sector 100 may include a preamble pattern 102 which allows the system to recover the timing and gain of the written servo data. Preamble pattern 102 is typically followed by a servo address mark (SAM) 104 which is the same for all servo sectors. SAM 104 is then followed by encoded servo Gray data 106, and Gray data 106 is followed by one or more burst demodulation fields 108. Gray data 106 may represent the track number/cylinder information and provides coarse positioning information for a read head traversing a magnetic storage medium. Burst demodulation field 108 provides fine positioning information for the read head traversing a magnetic storage medium. FIG. 1B shows the aforementioned servo data sector 100 incorporated as part of data sectors 170 distributed across a number of tracks 160 that extend in a radial pattern around a magnetic storage medium 150.
In an ideal case, a read/write head assembly traverses an individual track over alternating servo data sectors and user data sectors. As the read/write head assembly traverses the servo data sectors 100, a SAMFOUND signal is generated providing an indication of the location of the read/write head assembly in relation to magnetic storage medium 150. When a SAMFOUND signal is generated, the time interval from the last SAMFOUND signal is used to determine whether a disk lock clock is synchronized to the placement of servo data sectors 100 on storage medium 150. Where the disk lock clock is not properly locked, it is increased or decreased by an error amount indicated by the difference between the expected timing between consecutive SAMFOUND signals and the actual timing. This clock adjustment is performed once for each servo data sector 100.
Because adjustment of the disk lock clock is performed once per servo data sector with a step frequency change imposed to correct any error, the best that such an approach can achieve is to reduce the frequency offset of any given bit within the user data by one-half of the identified error. In the past, such an approach has been adequate to format overhead and to generally allow for system operation. However, as data detector technology continues to improve which allows for operation at lower signal to noise ratios, the loss of lock performance are becoming increasingly difficult to meet.
Hence, for at least the aforementioned reasons, there exists a need in the art for advanced systems and methods for accessing a magnetic storage medium.